1. Field of the Invention
This invention relates to a fine adjusting device for fine adjustment of the position of an object. More particularly, it relates to a two-directional fine adjusting device which makes it possible to move an object to any desired position on a two-dimensional plane and to precisely locate the object to the position.
2. Description of the Prior Art
Purely mechanical as moving mechanisms for finely adjusting the position of an object, have heretofore been generally employed. In such purely mechanical fine adjusting devices, however, mechanical play inevitably exists in the joint portions of the mechanical elements, such as the feed screw portion and carriage portion. This leads to the disadvantage that the play in successive elements adds up to cause a great positioning error. Further, the carriage is held by V-grooves and balls. Because of liminations on the accuracy of finishing of the V-grooves, the arrangement of the balls, etc., it is next to impossible to achieve movement of a sample with the required degree of linearity, and as a result accurate fine adjustment and positioning are difficult to attain.
In order to solve the problems of the purely mechanical fine adjusting device, novel devices which can carry out movements of very small units at high accuracy by employing only electrical signals have been proposed in Stanford Research Institute (hereinbelow, abbreviated to "SRI"): Physical Electronics Research Brief, No. 17, June 1975; Japanese Official Patent Gazette: Patent Application Publication No. 12497/1976 entitled "Step Fine Adjusting Device"; etc. The principle employed is characterized in that, by exploiting a very small expansion or contraction of a member having a counter piezoelectric effect which arises when a voltage is applied to the member, a desired fine adjusting motion is conducted purely electrically.
Hereunder, before presenting an explanation of this invention, an invention of Japanese Patent Application No. 60017/1976 entitled "Fine Adjusting Device" which has previously been proposed by the present inventors and which is now pending in Japan (not yet laid open) will be described with reference to FIG. 1. In the figure, numerals 10, 10' designate expansible and contractible members which employ a material presenting a counter piezoelectric effect (the effect in which the material expands or contracts by applying a voltage thereto). Such members are made of piezoelectric ceramics whose electromechanical coupling coefficient is great. In order to obtain the maximum counter piezoelectric effect, the members are shaped into cylinders. Of course, the cylindrical shape is not restrictive; the piezoelectric material in any other desired shape, such as a prismatic shape and flat shape, may be employed. While two separated counter piezoelectric members 10, 10' are used in this example, it is needless to say that an integral counter piezoelectric member may be adopted in view of the function. Electrodes for applying a voltage, 10A, 10'A and 10B, 10'B are respectively deposited on the inner and outer peripheral surfaces of the counter piezoelectric members 10, 10'. A variable DC power source E.sub.3 is connected between the inner and outer electrodes through a switch S.sub.3. The counter piezoelectric members 10, 10' lengthen (or shorten) in the axial direction in proportion to the voltage applied between the inner and outer electrodes. That is, the switch S.sub.3 and the variable DC power source E.sub.3 constitute electric signal generating means for lengthening or shortening the counter piezoelectric members 10, 10'. Numeral 13 indicates a mount which supports the counter piezoelectric members 10, 10' and which is anchored onto a fixed base 18. One end of each counter piezoelectric member 10, 10' is fixed to the mount 13 by a binder 11B, 11'B through an insulator ring 12B, 12'B. Shown at 19, 19' are sliders which are attached to the other end parts of the counter piezoelectric members 10, 10'. They are made of blocks of a conductive material 14, 14'on which semiconductor material layers 16, 16' are deposited. The slide members 19, 19' are respectively fixed to the end parts of the counter piezoelectric members 10, 10' by binder portions 11A, 11'A through insulator rings 12A, 12'A. The counter piezoelectric members 10, 10' and the slide members 19, 19' are disposed bilaterally symmetrically with respect to the mount 13, respectively. While, in the above explanation, the slide members 19, 19' are constructed of the blocks of a conductive material 14, 14' and attractors which are made of the semiconductor material layers 16, 16' fixed to the blocks by the conductive binder portions 15, 15', an insulator material may be used for the attractors instead of the semiconductor material as taught in the foregoing literature of SRI. Numeral 17 represents a movable plate, for example, a flat plate, made of a conductive material. DC power sources E.sub.1, E.sub.2 are connected between the flat plate 17 and the conductive material blocks 14, 14' of the slider members 19, 19' through switches S.sub.1, S.sub.2, respectively. When voltages are applied between the flat plate 17 and the conductive material blocks 14, 14' of the slide members 19, 19' by closing the switches S.sub.1, S.sub.2, great electrostatic attractive forces (i.e., coulomb forces) act between both the constituents 17 and 14, 14' with the semiconductor material layers 16, 16' intervening therebetween. Thus, the slide members 19, 19' are attracted and fastened to the flat plate 17, and a desired location of the flat plate 17 is fixed. That is, the switches S.sub.1, S.sub.2 and the DC power sources E.sub.1, E.sub.2 which are connected between the slider members 19, 19' and the flat plate 17 constitute electric signal generating means for attracting and fastening the flat plate 17 and the slide members 19, 19'. In the device constructed as stated above, the electrically secured states between the flat plate 17 and the slide members 19, 19' fixed to the end parts of the counter piezoelectric members 10, 10' are alternately released, and the counter piezoelectric members 10, 10' are lengthened (or shortened) in the meantime, whereby the flat plate 17 can be moved as will be stated later. That is, the flat plate which is a subject to be finely adjusted (or an object which is placed on the flat plate) can be easily moved.
Hereunder, the moving operation of the device shown in FIG. 1 will be described with reference to FIGS. 2-a to 2-g. In these figures, in order to facilitate understanding, the insulator rings 12A, 12B, 12'A, 12'B, the portions of a binder 11A, 11B, 11'A, 11'B, the portions of a conductive binder 15, 15' and the semiconductor material layers 16, 16' are omitted from the illustration. When the slide members 19, 19' are located (attracted and fastened to the flat plate 17), they are illustrated in contact with the lower surface of the flat plate 17. Conversely, when they are released from the location, they are illustrated in separation from the lower surface of the flat plate 17.
Now, consider as the reference a state under which all the switches S.sub.1, S.sub.2 and S.sub.3 are closed as in FIG. 2-a. In this state, each of the cylindrical counter piezoelectric members 10, 10' presents an elongation .DELTA. proportional to the applied voltage E.sub.3 in the axial direction by the counter piezoelectric effect. Both the slide members 19, 19' at both the ends of the members 10, 10' are located by the coulomb forces which act between the members 19, 19' and the flat plate 17. When the switch S.sub.1 is firstly opened from this state, the coulomb force which has existed between the slide member 19 and the flat plate 17 disappears, and the restraint between the slide member 19 and the flat plate 17 is released as shown in FIG. 2-b. When the switch S.sub.3 is subsequently opened, the elongation .DELTA. of each of the counter piezoelectric members 10, 10' disappears. Then, the slide member 19' moves by .DELTA. leftwards as shown in FIG. 2-c, and simultaneously, also the flat plate 17 moves by .DELTA. leftwards. Thereafter, the switch S.sub.1 is closed, to attract and fasten the slide member 19 to the flat plate 17 as shown in FIG. 2-d. At the next step, the switch S.sub.2 is opened to release the restraint of the slide members 19' as shown in FIG. 2-e. When the switch S.sub.3 is subsequently closed, each of the counter piezoelectric members lengthens by .DELTA. again. Then, as shown in FIG. 2-f, the slide member 19 moves by .DELTA. leftwards, and therewith, the flat plate 17 further moves by .DELTA. leftwards. When the switch S.sub.2 is closed here, the slide member 19' is again located, and a state in FIG. 2-g which is the same as the reference state in FIG. 2-a is established. In this case, however, the flat plate 17 has moved leftwards by 2.DELTA. from the original position.
By repeating such switching operation, the flat plate 17 can be moved step by step leftwards for every unit elongation 2.DELTA. of the counter piezoelectric members 10, 10'. In the case where conversely, the flat plate 17 is to be moved rightwards, the opening and closing sequence of the switches S.sub.1, S.sub.2 and S.sub.3 may be made quite the converse to the above. Such a switching operation can be conducted with a simple electric circuit, and moreover, it can be readily automated. As to the electric signal generating means, it is needless to say that pulse signal sources synchronized with one another may be employed as the power sources E.sub.1, E.sub.2 and E.sub.3 and that the switches may be ommitted. In such case, the speed of the stepping movement can be varied as desired by varying the recurrence period of the pulses.
The fine adjusting device based on the principle described above involves no mechanical play, and therefore, has the advantage that the accuracy of fine adjustment and the accuracy of positioning are remarkably high. However, in the case where the object is to be moved in any desired direction on a two-dimensional plane by such principle of fine adjustment, the following problems take place. By way of example, a construction is considered wherein two of the unidirectional fine adjusting devices as described above are provided, and one of the devices is placed on the other, whereby the one device is used for fine adjustment in the X-axial direction and the other device for fine adjustment in the Y-axial direction. In this case, the simultaneous movements in the X-axial direction and Y-axial direction are possible, but there is the disadvantage that the whole apparatus becomes structurally complicated and large-sized. It is also proposed to attach two sets of counter piezoelectric members, extending in the X-axial and Y-axial directions, to the mount 13 of the foregoing fine adjustment device and to alternately execute the movements of the flat plate 17 in the X-axial and Y-axial directions, thereby to simplify the construction of the apparatus. In this case, since the X- and Y-directional movements cannot be carried out at the same time, there is the disadvantage that a long time is required for the necessary two-dimensional movement.